Do you need to tell your insurer about an extension?

Yes. The Consumer Insurance (Disclosure and Representations) Act 2012 makes disclosure a legal duty. You should notify your insurer before the work starts and again once it is complete, because an extension changes the rebuild cost, the room count, and the risk profile of your home.

What happens if you do not tell your insurer about an extension?

Non-disclosure can let the insurer refuse or reduce a claim, charge a back-dated premium, or void the policy entirely and keep your premiums, depending on whether it was careless or deliberate. A loss combined with an undisclosed extension is a claims refusal waiting to happen.

What is the difference between rebuild cost and market value?

Rebuild cost is what it would cost to demolish and reconstruct your home using current labour and material prices, while market value is what a buyer would pay, including the land. Buildings insurance covers the rebuild cost, not the market value, and the two can differ widely.

How much does an extension increase your rebuild cost?

Less than the full build cost, because much of an extension spend goes on fittings and finishes that count as contents rather than structure. The rebuild figure uses standardised construction rates for the structural and fabric elements, calculated through a tool such as the BCIS calculator.

Does buildings or contents insurance cover a fitted kitchen?

It depends on the insurer. Fixed fabric such as walls, glazing, and structural doors sits in buildings cover, while loose and removable items sit in contents. Fitted kitchen units are a grey area: some insurers treat them as fixtures and others as contents, so confirm in writing where yours draws the line.

Do bifold and sliding doors affect home insurance?

They can. Many insurers have minimum security requirements for large glazed openings and prefer doors certified to PAS 24, sometimes also Secured by Design. If your doors do not meet the required standard, the insurer may reduce or exclude a claim involving forced entry through them.

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Phase 8 · Completion · Task 04 of 05

Updating Your Home Insurance After an Extension

Your extension changes your rebuild cost and risk profile. Failing to tell your insurer could void your entire policy. Here's exactly what to do, when to do it, and what your insurer needs to know.

11 min readUpdated 2026Premium

Two-step timeline showing insurance notification at start of build and update after completion, with checklist items and rebuild cost calculation icons

Prerequisites

Complete these first

Your extension is finished. You've got bifold doors that actually open without sticking, a kitchen that doesn't look like a builder's site, and a list of snagging items you're slowly working through. At some point during all of this, your insurer needs to know what's happened to their insured property.

Most homeowners treat this as admin. It isn't. It's a legal obligation, and getting it wrong can leave you uninsured at the worst possible moment.

What this guide covers

01Why this isn't optional
02The two-step process
03What your insurer needs to know
04The gap period: practical completion without sign-off
05Rebuild cost: what you're actually insuring
06How premiums change
07Contents insurance: the part everyone forgets
08Security standards for new doors
09How to make the update
10If your insurer won't continue cover
11The cost of doing nothing

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